Conventionally, predominant condenser microphones are microphones in which components, such as a diaphragm, a fixed electrode, and the like separately manufactured by a mechanical processing or the like are incorporated, as disclosed in Patent Document 1. These microphones are called ECMs (Electret Condenser Microphones), and miniaturization thereof has been tackled. As a result, a product having a diameter of 6 mm and a thickness of 1 mm and a product having a diameter of 4 mm and a thickness of 1.5 mm, and the like have been on sale. However, an ECM of the type disclosed in Patent Document 1, which uses mechanically-processed components, encounters difficulty in miniaturization.
A processing technology applying a semiconductor integrated circuit fabrication method, which is different from the conventional mechanical processing, is called a MEMS technology or a micro machining technology and is effective in miniaturization of microphones. Under the circumstances, microphone manufacturing methods using the MEMS technology have been proposed. For example, Patent Document 2 discloses a method of manufacturing a microphone with no electret with the use of the MEMS technology.    Patent Document 1: Japanese Patent Application Laid Open Publication No. 11-187494A    Patent Document 2: Japanese Patent Application Laid Open Publication No. 2003-78981AProblems that The Invention is to Solve
An electret condenser microphone having the structure disclosed in Patent Document 2, however, involves the following problems.
Namely, since the condenser and a drive circuit element, such as an IC are connected to each other with the use of a bonding wire, electric loss occurs in the bonding wire.
Further, as the condenser is reduced in size, the back air chamber integrally formed with the condenser is also reduced in size, degrading high-frequency characteristic of the microphone with the reduced back air chamber. As a result, a microphone exhibiting excellent performance cannot be manufactured.
The present invention has been made in view of the foregoing and has its object of providing an electret condenser microphone having a structure excellent in high-frequency characteristic even when miniaturized.
Means for Solving the Problems
To attain the above object, an electret condenser microphone according to the present invention includes: a substrate in which an opening is formed; an electret condenser connected to one face of the substrate so as to close the opening and having an acoustic hole and a cavity; a drive circuit element connected to the one face of the substrate; and a case mounted over the substrate so as to cover the electret condenser and the drive circuit element, wherein electric contact is established at a joint part between the electret condenser and the substrate, the acoustic hole communicates with an external space through the opening, and the cavity and an internal region of the case serve as a back air chamber for the electret condenser.
Effects of the Invention
In the present invention, electric contact between the substrate and the electret condenser is established at a mechanical contact part therebetween, in other words, the substrate and the electret condenser are connected to each other electrically without using a wire bonder, suppressing parasitic capacitance and noise occurrence caused due to the presence of the bonding wire. This enhances the high-frequency characteristic of the electret condenser. Further, the substantial volume of the back air chamber of the electret condenser can be increased by utilizing the space (the internal region of the case) formed by the case that covers the electret condenser, so that the high-frequency characteristic of the condenser can be enhanced even when the electret condenser is miniaturized.
As described above, according to the present invention, a small-size electret condenser microphone excellent in high-frequency characteristic can be provided.